Radio LAN system implementing simultaneous communication with different types of information and communication method for the same

ABSTRACT

A radio LAN (Local Area Network) system includes an access point and a mobile or a fixed station each having a physical layer implemented by a direct spread spectrum system. The LAN system uses different spread codes, maintains transmission power semi-fixed, and selects a frequency and a frequency band in accordance with the kind and amount of information. A data link layer above each physical layer includes an LLC (Logical Link Control) sublayer and an MAC (Media Access Control) sublayer. The MAC sublayer uses a CDMA (Code Division Multiple Access) system as an access system for thereby implementing a data structure in accordance with the kind and amount of information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority of U.S. patentapplication Ser. No. 10/131,143, filed Apr. 25, 2002, now U.S. Pat. No.7,058,113 of which it is a continuation.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a radio LAN (Local Area Network) systemand a communication method therefor.

2. Description of the Background Art

The radio LAN system is advantageously applicable to private premises inwhich an access point forms a service area and communicates withstations lying in the service area by radio. The communication method isadvantageously applicable to a multimedia communication procedure.

A radio LAN system constructed in private premises has customarily useda system prescribed by IEEE (Institute of Electrical and ElectronicsEngineers) 802.11b. This system is unique in that a direct spreadspectrum scheme is applied to a radio system and in that a CSMA/CA(Carrier Sense Multiple Access/Collision Avoidance) scheme is applied toa multiplexing system. The CSMA/CA scheme is desirable becausetransmitted power in a radio LAN system is generally far greater thanreceived power and cancels received power to thereby obstruct collisiondetection.

The CSMA/CA scheme has two different access systems, i.e., a DCF(Distributed Coordination Function) access system and a PCF (PointCoordination Function) access system. The DCF access system uses theconcept of LAN and does not need an access point, which the PCF accesssystem needs. Today, the direct spread spectrum system is applied tocellular phones because it is highly resistive to noise and interferenceand desirable in secrecy.

On the other hand, an access point or radio LAN base station and mobilestations are sometimes constructed into a single radio LAN system. Thiskind of radio LAN system has a single spread code and therefore uses aCSMA/CD (Carrier Sense Multiple Access/Collision Detection) scheme as amultiplexing system. The CSMA/CD scheme causes any one of the stationsto make an access after determining whether or not another station isemitting a radio wave. Therefore, a transmission time includes acollision detection time.

The CSMA/CD system has the following problems left unsolved. Thecollision detection time, among others, limits the effectivetransmission rate in a single system to only about 70% of a transmissionrata available with a communication path, as known in the art. Inaddition, additional information contained in overheads reduces theamount of information to be sent.

Assume that different types of information, e.g., real-time voiceinformation and usual file data exist together. Then, the CSMA/CD systemtransmits the different types of information by the same procedure.Consequently, voice information, needing real-time communication, issometimes forced to wait until the end of transmission of file data.More specifically, voice information is apt to be delayed and thereforediscontinuous in speech.

Further, the CSMA/CD system lacks an error correcting function althoughhaving an error detecting function in the communication procedure. It istherefore a common practice with the CSMA/CD system to assign thecorrection of an error having occurred in a radio section or interfaceto an upper-layer communication procedure. Usually, the error correctionis implemented by a re-transmitting function available with anupper-layer communication procedure. However, delay ascribable tore-transmitting is not allowable when it comes to voice information thatmust be real-time. Consequently, interruption of voice informationfrequently occurs e.g. in private premises in which a communication pathis often disconnected or the strength of a radio wave varies due to themovement of a speaker.

The only way available for reducing the interruption of voiceinformation is decreasing the service area of each access point andguaranteeing received field strength or increasing the output power ofeach terminal. However, increasing the output power of each terminalbrings about interference with another terminal.

As stated above, even when the CSMA/CD scheme is applied to a radio LANsystem, it is difficult to realize simultaneous transmission of voiceinformation and file data with the LAN system due to the delayparticular to the CSMA/CD scheme and errors ascribable to the varyingradio wave environment in a radio section.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a radio LAN systemcapable of transmitting, with quality comparable with that of a wiredLAN system, real-time information and non-real-time information at thesame time, and a communication method for the same.

In accordance with the present invention, a radio LAN system comprisesan access point forming a limited service area and a station present inthe limited service area for transmitting by radio information signalsbetween the access point and the station within the service area. In theradio LAN system, the access point and station each include atransmitter for spreading the information signal with a direct spreadspectrum system, which spreads the frequency of the information signal,and transmitting the resulting spread information signal. The accesspoint and station each further include a receiver for receiving thespread information signal and inversely spreading the spread informationsignal. The transmitter includes a plurality of information transmittingcircuits and a transmission controller. The information transmittingcircuits each multiply, in the direct spread spectrum system, theinformation signal and particular one of a plurality of spread codes.The transmission controller selects, in accordance with at least eitherone of the kind and amount of the information signal, one of frequencybands and frequencies respectively assigned to the informationtransmitting circuits and one of packets to use for the transmission ofthe information signal, and maintains transmission power of the spreadinformation signal semi-fixed. The receiver includes a plurality ofinformation receiving circuits and a receipt controller. Each of theinformation receiving circuits detects the synchronization of theinformation signal received and multiples the information signaldetected by particular one of a plurality of codes for inversespreading. The information receiving circuits determine a correlationbetween the resulting multiplied information signals to thereby restorethe information signal originally sent from the transmitter. The receiptcontroller maintains the received power of each spread informationsignal output from each of the information receiving circuitssemi-fixed, and guarantees the level of the spread information signal.The access point further includes a first interface for connecting theaccess point to a wired LAN system. The station further includes asecond interfacing circuit for connecting the station to either one of apublic switched telephone network and an apparatus configured to processthe information signal.

Also, in accordance with the present invention, a method of transmittinginformation signals by radio between an access point and a stationpresent in a limited service area in a radio LAN system begins with astep of setting up, as an access system between the access point and thestation, a CDMA (Code Division Multiple Access) using a plurality ofspread codes for spreading the information signal. The transmissionpower of the information signal spread is maintained semi-fixed.Subsequently, in accordance with the kind and amount of the informationsignal, a frequency band and a frequency to be assigned to theinformation signal and the structure of a packet for transmitting theinformation signal are selected. Thereafter, the information signal istransmitted in accordance with a transmission procedure.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the present invention will become moreapparent from consideration of the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1 is a schematic block diagram showing the general layeredstructure of a radio LAN system embodying the present invention;

FIG. 2 is a schematic block diagram showing an access point included inthe illustrative embodiment;

FIG. 3 is a schematic block diagram showing a specific configuration ofa transmission controller included in the access point;

FIG. 4 is a schematic block diagram showing a specific configuration ofa station also included in the illustrative embodiment;

FIG. 5 shows a total system including the illustrative embodiment of theradio LAN system and a wired LAN system;

FIGS. 6A-6D show packets unique to the illustrative embodiment;

FIG. 7 shows a relation between a data packet transferred in theillustrative embodiment and overheads added thereto;

FIG. 8 is a timing chart demonstrating the transmission of CH (channel)packets for control particular to the system of FIG. 5;

FIG. 9 is a timing chart showing a relation between spread codes basedon the kind of the packed used in the illustrative embodiment;

FIG. 10 is a timing chart demonstrating transmission of CH packets forcontrol in an application in which the system of FIG. 5 includes aplurality of access points; and

FIG. 11 shows an alternative embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1 of the drawings, a radio LAN system embodying thepresent invention is generally designated by the reference numeral 10.It is to be noted that FIG. 1 shows only part of the radio LAN system 10relevant to the understanding of the present invention. Signalsappearing in the LAN system 10 are designated by reference numeralsattached to connection lines on which they appear. As shown, the radioLAN system 10 covers a service area 12 including an access point 14 anda station 16.

The access point 14 includes a physical layer 14 a, a data link layer 14b and a network layer 14 c arranged in a hierarchical structure.Likewise, the station 16 includes a physical layer 16 a, a data linklayer 16 b and a network layer 16 c arranged in a hierarchicalstructure. The physical layers 14 a and 16 a both use the direct spreadspectrum system as a radio system and have a plurality of spread codes.The physical layers 14 a and 16 a prescribe electrical, mechanical andother rules.

The data link layers 14 b and 16 b, lying above the physical layers 14 aand 16 a, respectively include an LLC (Logical Link Control) sublayerand an MAC (Media Access Control) sublayer, generally 140, and an LLCsublayer and an MAC sublayer, generally 160. The LLC sublayers in thedata link layers 14 b and 16 b mediate between various kinds of MACsublayers 140 and 160 and the associated network layer 14 c or 16 c,respectively, so as to absorb differences in access control. The MACsublayers 140 and 160 each prescribe the construction of a data linklayer packet (frame), packet transfer procedure, error detecting methodand so forth. Although CSMA/CA (Carrier Sense Multiple Access withCollision Avoidance) is customary with MAC layers for a radio LANsystem, the illustrative embodiment uses the CDMA for a multiplexingpurpose.

In the illustrative embodiment, transmission power is “semi-fixed” inlevel at each of the access point 14 and station 16. More specifically,the illustrative embodiment sets the upper limit level of transmissionpower, but does not strictly limit channel-by-channel power. However,the access point 14 and station 16 each control the transmission powerof the entire LAN system 10 in such a manner as to guarantee receivedfield strength.

The access point 14 is connected to an existing LAN, not shown, via asignal line 142. The station 16 is connected to a public telephonenetwork or a personal computer or similar data processing terminal via asignal line 162. How the LAN system 10 is connected to the surroundingnetwork and data processing terminal will be described specificallylater.

FIG. 2 shows a specific configuration of the access point 14. As shown,the access point 14 includes an antenna 144, a DUP (antenna DUPlexer)146, an adder 148, a transmitter 150, a receiver 152, a LAN controller154, a LAN I/F (InterFace) 156, and a power supply 158. The antenna 144is a linear antenna effectively radiating transmission power output fromthe access point 14 and receiving an electromagnetic wave from thestation 16. The DUP 146 is capable of separating a signal to be radiatedvia the antenna 144 from a signal coming in through the antenna 144 atthe same time. The DUP 146 delivers the above signals to appropriateportions of the circuitry shown in FIG. 2. The adder 148 adds datasignals 150 a and 150 b output from the transmitter 150.

In the illustrative embodiment, the transmitter 150 has two identicaldata transmitting sections 150A and 150B although the crux is that ithas two or more different transmitting sections. The followingdescription will concentrate on the data transmitting section 150A byway of example. The data transmitting section 150A includes atransmission controller 50, a transmission BB (Base Band) circuit 52, atransmission IF (Intermediate Frequency) circuit 54, an AGC (AutomaticGain Controlled) amplifier 56, a BPF (Band Pass Filter), and a poweramplifier 60.

The transmission controller 50 adds overheads to data fed from the LANcontroller 154 while checking the data for errors. For this purpose, asshown in FIG. 3 specifically, the transmission controller 50 includes aformat storage 50 a, a data storage 50 b, and a CPU (Central ProcessingUnit) 50 c which are interconnected to each other by a bus 50 e asdepicted. It is to be noted that the configuration shown in FIG. 3similarly applies to the receipt controller 68 and a controller includedin the station 16, which will be described specifically later.

In FIG. 3, the format storage 50 a includes a ROM (Read Only Memory)adapted to store format information relating to the overheads, aprocessing procedure based on the format information, parameters set inthe physical layer 14 a, FIG. 1, and so forth. The data storage 50 bincludes a RAM (Random Access Memory) for temporarily storing the datafed from the LAN controller 154, FIG. 2. The CPU 50 c processes the datastored in the data storage 50 b in accordance with the processingsequence stored in the format storage 50 a. The format storage 50 aadditionally stores a particular frequency band to be used, and aparticular frequency to be used and other information assigned to eachkind of information, e.g., voice or file data. The CPU 50 c is clockedby a quartz oscillator 50 d. The format storage 50 a, data storage 50 band CPU 50 c are interconnected by the bus 50 e and signal lines 50 f,50 g and 50 h.

The CPU 50 c, in operation, reads out a frequency and a frequency bandmatching with the kind and quantity of data as well as the processingprocedure from the format storage 50 a. The CPU 50 c fetches the data 50f including the fetched information from the format storage 50 a via thesignal line 50 h. The CPU 50 c also reads out the data, labeled 50 g,from the data storage 50 b and processes the data. Subsequently, the CPU50 c outputs the processed data to the bus 50 e on the signal line 50 h.The transmission controller 50 delivers the processed data 50 h to thetransmission BB circuit 52.

Referring again to FIG. 2, the transmission BB circuit 52 includes acode generator and a multiplier although not shown specifically. Thecode generator generators a spread code. The multiplier multiplies theinput data 50 h by the spread code. While the transmission BB circuit 52may include a plurality of code generators, the data transmittingsection 150A uses a single spread code. A plurality of data transmittingsections will be used when simultaneous multiple access is required.

More specifically, the data 50 h input to the transmission BB circuit 52lies in a narrow frequency band. The transmission BB circuit 52multiplies the data 50 h by the spread code lying in a far broaderfrequency band than the data 50 h, thereby outputting a spread signal 52a having a broad frequency band. The spread signal 52 a is input to thetransmission IF 54. Further, the transmission BB circuit 52 feeds acontrol signal 52 b to the AGC amplifier 56 in order to guarantee thefield strength of a signal to be sent that is above a preselected level.

The transmission IF 54 includes an IF generating circuit and a frequencyup-converting circuit although not shown specifically. The IF generatingcircuit generates a carrier signal. The up-converting circuit multipliesthe base-band spread signal 52 a by the carrier signal. With thisconfiguration, the transmission IF 54 executes frequency conversion withthe spread signal 52 a for thereby shifting the baseband to a higherfrequency band. To set an intermediate frequency, the transmission IF 54uses a frequency selected by the transmission controller 50 by way ofexample. An up-converted spread signal 54 a output from the transmissionIF 54 is input to the AGC amplifier 56. The AGC amplifier 56 amplifiesthe spread signal 54 a to a preselected level for thereby outputting aspread signal 56 a with a guaranteed level. The spread signal 56 a isinput to the BPF 58. If desired, the transmission controller 50 may beadapted to control the signal level.

In the CDMA system, the BPF 58 performs TDD (Time Division Duplex) modeoperation with respect to a fixed frequency band. The BPF 58 uses afrequency band selected by the transmission controller 50, although notshown specifically. A relation between the BPF 58 and the TDD mode willlater be described more specifically. The BPF 58 feeds the resultingspread signal 58 a confined in the preselected frequency band to thepower amplifier 60. The power amplifier 60 amplifies the power of theinput spread signal 58 a. The resulting output of the power amplifier 60is delivered to the adder 148 as the output signal 150 a of the datatransmitting section 150A.

In the illustrative embodiment, the receiver 152 also includes two datareceiving sections 152A and 152B although the crux is that it includestwo or more receiving sections. Because the data receiving sections 152Aand 152B are identical in configuration, the following description willconcentrate on the data receiving section 152A by way of example. Thedata receiving section 152A is made up of an AGC amplifier 62, a receiptIF 64, a receipt BB circuit 66, and a receipt controller 68. Basically,the data receiving section 152A executes processing inverse to theprocessing of the data transmitting section 150A. The DUP 146 separatesa received spread signal 14 e from a spread signal 14 d to be sent outand inputs the signal 14 e to the receiver 152.

The AGC amplifier 62 shifts the received spread signal 14 e to a levelhigher than a preselected level in accordance with a control signal 66 aoutput from the receipt BB circuit 66. A spread signal 62 a with theshifted level is output from the AGC amplifier 62 to the receipt IF 64.It is to be noted that the spread signal 62 a lies in a frequency bandfixed by the station 16, FIG. 1, beforehand, as will be described indetail later.

The receipt IF 64 includes an IF generating circuit and a frequencydown-converting circuit although not shown specifically. The IFgenerating circuit generates a carrier signal. The frequencydown-converting circuit multiplies the spread signal 62 a by the carriersignal for thereby lowering the frequency of the spread signal 62 a tothe base band. With this configuration, the receipt IF 64 lowers thebroadened frequency band of the spread signal 62 a to the base band,thereby outputting a spread signal 64 a having its center frequency inthe base band. The spread signal 64 a is input to the receipt BB circuit66.

The receipt BB circuit 66 includes a synchronization detecting circuit,a code generating circuit, a multiplier and an LPF (Low-Pass Filter)although not shown specifically. The synchronization detecting circuitdetects the synchronization of the spread signal 64 a. The codegenerating circuit generates a spread code. The multiplier multipliesthe spread signal 64 a by the spread code. The spread code output fromthe code generating circuit is identical with a spread code generated bya transmitting station having transmitted the spread signal. The LPFfinds out correlation with the output of the multiplier to therebyoutput only a base band signal 66 a correlated. The LPF can thus outputonly the necessary signal because the other signals without anycorrelation are zeros, and yet does not effect the necessary signal atall. The receipt BB circuit 66 delivers the base band signal or receiveddata 66 a to the receipt controller 68.

The receipt controller 68 may be identical in hardware configurationwith the transmission controller 50 shown in FIG. 3. The receiptcontroller 68 removes overheads from the received data 66 a. The receiptcontroller 68 may be adapted to additionally control the level of theAGC amplifier 62, if desired. The receipt controller 68 delivers theresulting received data 68 a to the LAN controller 154 as the output ofthe data receiving section 152A. The other data receiving section 152Bfeeds received data 68 b to the LAN controller 154 in the same manner asthe data receiving section 154A.

The LAN controller 154 is connected to the LAN I/F 156 by a signal line154 c. The LAN controller 154 controls transmission and receipt from anexisting, wired LAN system via the LAN interface 156. Specifically, data154 a and 154 b received from the wired LAN system are input to thetransmitter 150. Then, the LAN controller 154 analyzes and removesoverheads added to the data 154 a and 154 b by the wired LAN system. Onthe other hand, the data 68 a and 68 b are delivered from the receiver152 to the wired LAN system. Then, the LAN controller 154 analyzesoverheads used in the radio LAN system 10, which includes the accesspoint 14 and station 16, and generates overheads matching with the wiredLAN system in accordance with the result of analysis.

The LAN I/F 156 is connected to the wired LAN system via the signal line142 and transmits and receives data to and from the wired LAN system.The LAN I/F 156 executes processing matching with the electrical andmechanical connection of the physical layer of the wired LAN system.

The power supply 158 feeds a particular voltage 158 c to each section ofthe access point 14. The power supply 158 selectively receives a powersupply signal 156 a or 156 b from the LAN I/F 156 or a power supplyterminal 164, respectively.

Reference will be made to FIG. 4 for describing a specific configurationof the station 16. The station 16 includes some constituents identicalwith those of the access point 14; the former constituents with the samelegends as the latter constituents will not be described in order toavoid redundancy. As shown, the station 16 is generally made up of anantenna 166, a DUP 168, a radio section 170, a base band section 172, acontroller 174, an I/F 176, and a power supply 178.

The radio section 170 includes a transmitter 170A and a receiver 170B.The transmitter 170A includes a transmission IF 70, an AGC amplifier 72,a BPF 74, and a power amplifier 76. The receiver 170B includes an AGCamplifier 78 and a receipt IF 80. In the operation of transmission, thebase band section 172 delivers a spread signal 82 a to the transmitter170A. The transmitter 170A up-converts the spread signal 82 a to apreselected level, limits the frequency band of the spread signal 82 a,and then amplifies the power of the spread signal 82 a. The resultinghigh-frequency signal 16 d output from the transmitter 170A is deliveredto the DUP 168. In the operation of receipt, a received high-frequencysignal 16 e separated by the DUP 168 is input to the receiver 170B. Thereceiver 170B controls the level of the received signal 16 e to herebyproduce a down-converted signal 80 a. The AGC amplifiers 72 and 78respectively control the level in response to control signals 82 b and84 a, which are output from the base band section 172. Alternatively,the controller 174 may be adapted to control the AGC amplifiers 72 and78, if desired.

The base band section 172 includes a transmission BB circuit 82 and areceipt BB circuit 84 each having a spread code for identifying thestation 16. The controller 174 feeds a signal 174 a to the transmissionBB circuit 82. The transmission BB circuit 82 spreads the signal 174 afrom the base band to thereby produce a spread signal 82 a. The spreadsignal 82 a is in turn input to the radio section 170. The receipt BBcircuit 84 inversely spreads a signal 80 a input from the radio section170 and feeds the resulting signal 84 b to the controller 174.

The controller 174 is basically identical in configuration with thetransmission controller 50 described with reference to FIG. 3. The I/F176 delivers data 176 a to be sent to the controller 174. The controller174 a formats the data 176 a to match it to the radio LAN system 10,i.e., generates overheads to be added to the data 176 a and executeserror detection with the data 176 a. Formatted data 174 a is fed fromthe controller 174 to the base band section 172. The controller 174 maybe adapted to execute error correction in addition to error detection,if necessary. On the other hand, when the receipt BB circuit 84 feedsthe received signal 84 b to the controller 174, the controller 174separates a data packet 176 a included in the received signal 84 b. Morespecifically, the controller 174 removes the overheads used in the radioLAN system 10. The data packet 176 a is input to the I/F 176.

The I/F 176 electrically and mechanically matches the station 16 to anapparatus, not shown, connected to the station 16 while executingprocessings for transmission or receipt. For example, the I/F 176transmits and receives data 176 b or 176 c to and from a telephone or apersonal computer, not shown, connected to the station 16. As for thoseprocessings, the I/F 176 analyzes and removes overhead when receivingdata from the telephone or the personal computer or generates data(added overhead) when delivering the data to the telephone or thepersonal computer.

The power supply 178 receives a power supply voltage 178 a from theoutside of the station 16 and feeds a particular voltage and aparticular current, labeled 178 b, to each section of the station 16.

FIG. 5 shows a specific configuration of the radio LAN system 10. Asshown, the radio LAN system 10 covers a service area 12 in which asingle AP (Access Point) 14 and three STAs (STAtions) 18 a, 18 b and 18c are located by way of example. A PC (Personal Computer) 108 isconnected to the STA 18 a by a signal line 100. Another TEL (TELephone)110 is connected to the STA 18 b by a signal line 102. Another PC 112and a further TEL 114 are connected to the STA 18 c by signal lines 104and 106, respectively. A signal line 118 connects the AP 14 to a wiredLAN 116 constructed by the previously mentioned wired LAN system.Another signal line 122 connects the wired LAN 116 to another servicearea 120.

In the illustrative embodiment, the CDMA system is applied to each MACsublayer included in the radio LAN system 10, as stated earlier.Reference will be made to FIGS. 6A-6D for describing a control channel(CH) packet and a data CH packet used in the CDMA system. The data CHpacket is distinguished from a channel packet for data to be describedlater.

As shown in FIGS. 6A and 6B, two different control CH packets areprepared. The access point 14 generates a control CH packet 20, FIG. 6A,and sends it out to the station 16. The station 16 generates a controlCH packet 22, FIG. 6B, and sends it out to the access point 14. Thecontrol CH packet 20 has the following six fields:

-   -   field 20 a for frame synchronization (FS),    -   field 20 b assigned to ID information particular to the access        point 14 (AP_ID),    -   field 20 c assigned to information on channel numbers usable for        voice (V) and indicating n channels (V-CH INF.),    -   field 20 d assigned to information on channel numbers usable for        data (D) and indicating n channels (D-CH INF.),    -   field 20 e assigned to control information and indicating any        one of a location confirmation request, a new registration        request, a call request and channel release (CONTROL INF.) and    -   field 20 f assigned to a frame check sequence for error control        (FCS).

In the CONTROL INF. field 20 e, the location confirmation requestcommands the station 16 present in the service area 12 of the accesspoint 14 to answer the access point 14. The new registration requestcommands the station 16 newly entered the service area 12 to send aregistration request to the access point 14. The call request commandsthe station 16 to communicate. Those requests each include IDinformation unique to the station 16 and a CH number to answer; the IDinformation includes address information as well as other information.

The other control CH packet 22 has the following four fields:

-   -   field 22 a for frame synchronization (FS),    -   field 22 b assigned to the ID information of the station 16        (STA_ID),    -   field 22 c assigned to control information and indicating any        one of a location confirmation request acknowledgement, a new        registration request acknowledgement, a call request        acknowledgement, a data communication request and channel        release (CONTROL INF.), and    -   field 22 d assigned to a frame check sequence for error control        (FCS).

In the CONTROL INF. field 22 c, the location confirmationacknowledgement and new registration acknowledgement are respectively ananswer to the location conformation request and an answer to the newregistration request received from the access point 14. The call requestacknowledgement is an answer to the call request received from theaccess point 14. The data communication request requests the accesspoint 14 to communicate. Channel release informs the access point 14 ofthe release of a channel.

Data CH packets will be described hereinafter, see FIGS. 6C and 6D. A CHpacket for data 24, FIG. 6C, has the following six fields:

-   -   field 24 a for frame synchronization (FS),    -   field 24 b assigned to destination ID information (D ID),    -   field 24 c assigned to source ID information (S ID),    -   field 24 d assigned to the number or the amount of data (NUM. OF        DATA),

field 24 e assigned to data the amount of which is indicated by thefield 24 d (DATA), and

-   -   field 24 f assigned to error control data (FCS).

The length of data stored in the DATA field 24 e is variable. The errorcontrol data is meant for the fields 24 b through 24 e.

A CH packet 26 for voice, which is the other data CH packet, has thefollowing five fields:

-   -   field 26 a for frame synchronization (FS),    -   field 26 b assigned to destination ID information (D ID),    -   field 26 c assigned to source ID information (S ID),    -   field 26 d assigned to data (DATA), and    -   field 26 e assigned to error control data (FCS).

The fields 26 a through 26 d are fixed in data length. Data in thefields 26 a through 26 d are implemented as an error correction code andsubjected to error correction and error detection in the field 26 e. Forerror correction, use is made of FEC (Forward Error Correction). Errorcorrection may not be executed at the beginning of communication, ifdesired.

The radio LAN system 10 including the access point 14 and station 16 isselectively connected to the wired LAN system 116, the TEL 110 or 114 orthe PC 108 or 112, as stated with reference to FIG. 5. Paying attentionto the CH packet 24 for data by way of example, a relation betweenoverheads generated at the various sections will be described withreference to FIG. 7.

Assume that the station 16 is connected to the TEL 110 or 114 or the PC108 or 112. Then, as shown in FIG. 7, part (a), overheads 30 a and 30 bparticular to the TEL or the PC are added to the head and tail of thedata field 24 e, respectively. In the station 16, the I/F 176 analyzesthe overheads 30 a and 30 b and then removes them. As shown in FIG. 7,part (b), considering the result of analysis, the controller 174generates the fields 24 a through 24 d and 24 f as overheads particularto the radio LAN system 10. The fields 24 a through 24 d and the field24 f are added to the head and tail of the data field 24 e,respectively. It is to be noted that, among the overheads, the fields 24b through 24 d are sometimes absent. The station 16 sends the CH packet24 with the overheads 24 a through 24 d and 24 f to the access point 14by radio.

At the access point 14, the receipt controller 68 analyzes the overheadsattached to the above CH packet 24, separates data, and then removes theoverheads particular to the radio LAN system 10. As shown in FIG. 7,part (c), considering the result of analysis, the LAN controller 154generates overheads 32 a and 32 b particular to the wired LAN 116 of thewired LAN system, which is connected to the radio LAN system 10. The LANcontroller 154 then adds the overheads 32 a and 32 b to the head andtail of the data field 24 e, respectively. The access point 14 sends theCH packet 24 with the overheads 32 a and 32 b to the wired LAN 116.

It will readily be seen that data can also be transferred from the wiredLAN 116 to the TEL 110 or 114 or the PC 108 or 112 via the radio LANsystem 10 when consideration is given to the relation between thegeneration and the removal of the overheads described above.

On the specific radio LAN system 10 shown in FIG. 5, the operationprocedure of the illustrative embodiment will be described hereinafter.In the radio LAN system 10, communication is held between one of theSTAs 18 a through 18 c and the other of the same either directly or byway of the AP 14. The procedure to be described assumes communicationeffected via the AP 14. After the power-up of the AP 14 and STAs 18 athrough 18 c, the STAs 18 a through 18 c each report the AP 14 that itis under the control of the AP 14, and requests authentication. Inresponse, the AP 14 authenticates the STAs 18 a through 18 c one by onein consideration of a particular frequency and a particular code (spreadcode) unique to the system. In addition, the AP 14 executesauthentication when the radio LAN system 10 is increased or reduced insize; otherwise, whether or not communication can be held would becomeundecided.

More specifically, at the time of authentication, the AP 14 determinescontrol information including a frequency, a chip rate and codeassignment in the physical layer. In the illustrative embodiment, the AP14 assigns a plurality of different control information to each of theSTAs 18 a through 18 c while giving a particular priority order to suchcontrol information. More specifically, assume that a period of time tobe occupied by a single station increases due to an increase in thenumber of stations or the amount of data to be interchanged. Then, theremay occur that a single combination of control information cannotimplement communication or that the effective transmission rate iscritically lowered. In light of this, the AP 14 assigns a plurality ofdifferent control information to each station, as will be described indetail with reference to FIG. 9 later.

Further, the AP 14 prevents the system from interfering with the systemof another access point as to frequency, frequency band and spread code.Management information is stored in the AP 14 before hand and fedtherefrom or is fed from a server or similar equipment connected to thewired LAN 116. Only the AP 14 supplies the STAs 18 a through 18 c lyingin the service area 12 with the management information.

The operation of the illustrative embodiment will be described morespecifically hereinafter. On power-up, the AP point 14 sends out thepreselected control CH packet 20 to each of the STAs 18 a through 18 clying in the service area 12. At this instant, the AP 14 sets semi-fixedtransmission power. This implements a guaranteed level below thesemi-fixed level for each of voice and data, while dividing the levelwithin the range below the upper limit. The level may be equally dividedor may differ from voice to data, as desired. The AP 14 repeatedly sendsout the control CH packet 20 either periodically or non-periodically.The period of packet transmission will be described more specificallylater.

On power-up, the STAs 18 a through 18 c each start monitoring as to thecontrol CH packet 20 to be received from the AP 14. Transmission poweris semi-fixed in the physical layer 16 a of each of the STAs 18 athrough 18 c as well, as stated earlier. More specifically, the STAs 18a through 18 c each monitor the field strengths of signals beingreceived at the frequencies of all control channels. Each of the STAs 18a through 18 c then selects a control CH channel having the highestfield strength. Subsequently, the STAs 18 a through 18 c each try codesynchronization with the control CH packet selected in order todetermine whether or not the control packet sent from the AP point 14can be received.

So long as the STAs 18 a through 18 c can receive signals havingsufficient field strength, the above monitoring should only continueover a period of time (or a monitoring time) that implements surechannel seizure. However, to reduce the monitoring time, the spread codefor control should preferably be about eleven-bit long. In this sense,Berger code unique to IEEE. Std. 802.11 is desirable.

If any one of the STAs 18 a through 18 c fails to receive data with thecontrol CH packet having the highest field strength, then the STAreceives data with another control CH packet having the second highestfield strength. The STA then sends an acknowledgement signal to theaccess point 14.

Subsequently, the AP 14 determines whether or not the STAs 18 a through18 c are present in the area 12 on the basis of the acknowledgements ofthe receipt of the control CH packet 20. More specifically, aftersending the control CH packet 20 to the service area 12, the AP 14determines whether or not it receives the acknowledgement signal Nconsecutive times from each of the STAs 18 a through 18 c. The AP 14determines that any one of the STAs 18 a through 18 c is present in theservice area 12 when received the acknowledgement signal N consecutivetimes from the STA; otherwise, the AP 14 determines that the STA hasleft the area 12. The number of times N is a natural number and may bethree by way of example.

In the illustrative embodiment, the STAs 18 a through 18 c each belongto either one of a fixed class and a mobile class. Assume that the STAs18 a through 18 c all belong to the fixed class, particularly that theyare limited to the fixed class beforehand. Then, a period 28, FIG. 8, atwhich the AP 14 sends out the control CH packet 20 is fixed, e.g., theAP 14 sends it once for an hour. FIG. 8, part (a), shows a timing atwhich the AP 14 sends out the control CH packet 20 to the STAs 18 athrough 18 c and a timing at which the former receives acknowledgementsignals (ACK) from the latter over the same channel. In FIG. 8, part(a), transmission and receipt are respectively shown above and belowlines representative of time.

The AP 14 has at least three different spread codes, as statedpreviously. The access point 14 sequentially sends the control CHpackets meant for the STAs 18 a through 18 c at times t₁, t₂ and t₃. TheSTAs 18 a, 18 b and 18 c send out ACK signals to the AP 14, as shown inFIG. 8, parts (b), (c) and (d), respectively. As soon as the AP 14receives the ACK signal from any one of the STAs 18 a through 18 c, itimmediately sends out another control CH packet to the next STA withoutany interval.

As for the mobile class, the AP 14 repeatedly sends out the control CHpackets to the STAs 18 a through 18 c at the period 28 of, e.g., severalhundred milliseconds. The AP 14 can therefore frequently locate the STAs18 a through 18 c. Further, the AP 14 can sufficiently deal with any oneof the STAs 18 a through 18 c entered the service area 12 and candetermine whether or not it has already been registered, as will bedescribed more specifically later.

Subsequently, the AP 14 sends out a new registration request to each ofthe STAs 18 a through 18 c existing in the area 12. In response, theSTAs 18 a through 18 c each send a new registration acknowledgementsignal to the AP 14. On receiving the new registration acknowledgementsignal, the AP 14 registers the STA having transmitted the signal. Inthis manner, the AP 14 locates the STAs 18 a through 18 c present in theservice area 12.

The CH packet 24 for data and CH packet 26 for voice will be describedmore specifically hereinafter. As shown in FIG. 9, part (a),specifically, the AP 14 has a plurality of spread codes a, b and c eachhaving a particular length. The STAs 18 a and 18 b, for example,respectively have the spread codes b and c, as shown in FIG. 9, parts(b) and (c), respectively. The spread codes a and b are assigned to datawhile the spread code c is assigned to voice. The spread codes a and band the spread code c are distinguished from each other on the basis ofwhether or not data is real-time data. In the illustrative embodiment,the distinction is done by each of the AP 14 and STAs 18 a and 18 b andis not prescribed specifically.

As shown in FIG. 9, a short unit packet length and a long unit packetlength are assigned to voice and PC data or similar data, respectively.In this manner, the AP 14 reduces the packet length not by sending outall channel information available with the AP 14, but by sending outonly two to three channel information. This is also true with thecontrol CH packet. In FIG. 9, transmission and receipt are respectivelyshown above and below the lines representative of time. Also, boxesabove the lines and boxes below the same indicate the unit lengths ofpackets transmitted and the unit lengths of packets received,respectively.

Subsequently, when any one of the STAs 18 a through 18 c accesses the APpoint 14, the AP 14 updates information on usable channels. The AP 14then sends out a data transmission request to the above STA by using theinformation on the control channels. In response, the STA accessed theAP 14 executes bidirectional data communication by using, among thechannels assigned to the previously stated data CH packet for voice orthe data CH packet for data, an idle channel with higher priority.

Assume that the TEL 110 or 114 or the PC 108 or 112 sends outend-of-communication information to one of the STAs 18 a through 18 cconnected thereto or that the STA in communication does not receive datafrom the AP 14 over a preselected period of time. Then, the STA incommunication sends forcible channel release information to theassociated TEL 110 or 114 or the associated PC 108 or 112 as well as tothe AP 14. The STA then releases the channel. The period of timementioned above may be about one minute.

On the other hand, assume that the AP 14 in the radio LAN system 10receives data 118 from the wired LAN 116. Then, the AP 14 determineswhether or not the destination for which the data 118 is meant is anyone of the STAs 18 a through 18 c present in the service area 12. If theanswer of this decision is positive, then the AP 14 sends out a callrequest to the destination for thereby calling the subject STA.

One of the STAs 18 a through 18 c having received the call request sendsout an acknowledgement signal to the access point 14 by using the usablechannel. At the same time, the STA reports the receipt of data to one ofthe TELs 110 and 114 and PCs 108 and 112 connected thereto. The reportshould only be suitably sent on the basis of communication protocolshared by the STA and the TEL or the PC. In response to the aboveacknowledgement, the AP 14 sends out the control CH packet to thesubject STA in order to indicate it to shift to the data CH packet. TheAP 14 then negotiates with the wired LAN 116 and subject STA as tocommunication connection for thereby setting up connection, and theneffects data communication.

Assume that the AP 14 or any one of the STAs 18 a through 18 c holdingcommunication in the radio LAN system 10 does not receive data over apreselected period of time, or that the STA holding communicationreceives the end-of-communication information from the TEL 110 or 114 orthe PC 108 or 112 connected thereto or does not receive any data fromthe AP 14 over the preselected period of time, e.g., about one minute.Then, the STA in communication sends out forcible channel releaseinformation to the TEL or the PC and AP 14. In response, the AP 14suitably transmits to the wired LAN 116 information indicative of forcedchannel release. On the other hand, when the AP 14 receives forciblechannel release information from the wired LAN 116, the AP 14 sends outchannel release information to the STA in communication and thenreleases the channel.

As shown in FIG. 9, communication in the radio LAN system 10 using theCDMA system selectively executes transmission and receipt on the samechannel. Because the CDMA system is free from interference betweencodes, transmission (down-going channel) and receipt (up-going channel)are duplexed between the AP 14 and one of the STAs 18 a through 18 csharing the same spread code with each other. For example, the AP 14shares the spread code b with the STA 18 a and shares the spread code cwith the STA 18 b, as shown in FIG. 9. In this case, the AP 14 switchestransmission and receipt between it and each of the STAs 18 b and 18 csuch that they do not overlap each other in each combination. This kindof bidirectional communication system will be referred to as a TDD (TimeDivision Duplex) mode hereinafter.

While the illustrative embodiment has concentrated on a single AP 14,the radio LAN system 10 may include a plurality of access points eachcovering a particular service area, as will be described hereinafter.FIG. 10 shows the transmission established by three APs 130, 132 and 134in parts (b), (c) and (d) thereof, respectively, by way of example. Asshown, the APs 130 through 134 each repeatedly sends out the respectivecontrol CH packet in particular time slots at a period T. The APs 130through 134 each monitor the respective service area to see if anystation is present. For example, a STA 130 a shown in FIG. 10, part (e),is located in the service area of the AP 130. The STA 130 a receivescontrol information contained in the control CH packet from the AP 130and then sends out an acknowledgement packet to the AP 130. Likewise,the AP 132 sends out the control CH packet in the time slots assignedthereto. STAs 132 a and 132 b respectively shown in FIG. 10, parts (f)and (g) both send out respective acknowledgement packets to the AP 132.

The APs 130, 132 and 134 send out the respective control CH packets atthe period T, as stated above. Therefore, when a station belonging to,e.g., the mobile class newly enters the service area of any one of theAPs 130 through 134, a period of time necessary for the station to beregistered at the service area is extended. The station, however, canselect the optimal access point for radio communication in a shorterperiod of time. Considering a tradeoff between the above two points, theillustrative embodiment allows the station to be registered in a periodof time substantially as short as conventional one.

As stated above, the illustrative embodiment allows each station toselect a particular channel in accordance with the content ofcommunication and selectively send real-time voice or non-real-timeusual data. Therefore, even when voice communication using a VoIP (Voiceover IP (Internet Protocol)) or similar IP network is applied to a radioLAN system, a delay ascribable to other types of communication areobviated. It follows that a radio LAN system achieves communicationquality comparable with the communication quality of a wired LAN system.

The illustrative embodiment further reduces the above delay byselectively using data CH packets in a radio section in accordance withthe amount and quality of information, e.g., voice or data. It followsthat not only an error detection sequence but also FEC can be executedwith packets for voice. The illustrative embodiment therefore freesradio LAN communication from the intermittent interruption of voice bycorrecting insignificant errors ascribable to momentary changes inelectric field, which are particular to radio communication, and therebyguarantees QoS (Quality of Service).

Furthermore, the illustrative embodiment is capable of varying not onlythe packet configuration but also the information transfer rate.Therefore, in a radio LAN system, it is possible to save the frequencyband by making the most of the advantages of the direct spread spectrum,which effects communication while maintaining a spread gain constant.The spread gain refers to a ratio of an information transfer rate to aspread code rate or chip rate.

Reference will be made to FIG. 11 for describing an alternativeembodiment of the present invention. As shown, this embodiment includesa radio LAN system 200 to which the TDD mode particular to IMT-2000(International Mobile Telecommunications-2000) is applied. IMT-2000belongs to a family of state-of-the-art mobile communication systems.The radio LAN system 200 is identical with the radio LAN system 10, FIG.5, except for the configuration and system of the service area 202. Thefollowing description will therefore concentrate on the configuration ofthe service area 202 dependent on an IMT-2000 AP 204.

Mobile stations of the IMT-2000 cellular phone system, which correspondto the stations, 206 and 208 are assumed to be located in the servicearea 202. A plurality of cellular phones are connectable to the AP 204.A PC 210 is shown as being connected to the mobile station 206 via anexternal interface, not shown, which is prescribed or recommended byIMT-2000. The mobile station 206 receives data 206 a from the PC 210 totransmit the data to the AP 204, and receives data from the AP 204.

The AP 204 may be connected to a wired LAN system 300 by a wired signalline 212. Also, the AP 204 may be connected to a radio access apparatus(simply radio apparatus hereinafter) 214, which uses another system, bya wired signal line 216. The radio apparatus 214 communicates withanother radio apparatus 218 by radio. The radio apparatus 218 isconnected to the wired LAN system 300 by a wired signal line 220.

The IMT-2000 radio LAN system 200 has most of the advantages of theprevious embodiment and in addition executes transmission power control,thereby further enhancing efficient use of limited channels. The mobilestations 206 and 208 each are connectable to a public switched telephonenetwork outside of the service area 202 and can be used in a VoIP modevia the radio LAN inside of the service area 202. It is to be noted thatthe mobile stations 206 and 208 should preferably be adaptive not onlyto an FDD (Frequency Division Duplex) mode customary with a publicswitched telephone network, but also to the TDD mode inclusive offrequency. The IMT-2000 specifications applied to the radio LAN system200 make it needless to newly develop, e.g., circuitry for dealing withbase band and LSI (Large-Scale Integration circuit) and thereforenoticeably reduces the apparatus cost.

The access points included in the illustrative embodiments are onlyillustrative and may be connected to a PBX (Private Branch Exchange)each. Further, in the case of a radio LAN system constructed at theuser's private premises, each access point may be connected to an ADSL(Asymmetric Digital Subscriber Line) or an ISDN (Integrated ServicesDigital Network). In addition, the radio LAN system may include the CDMAaccess point and IMT-2000 access point of the illustrative embodimentsfor selectively communicating with CDMA stations or IMT-2000 cellularphones.

The illustrative embodiments insure the individuality of each type ofcommunication on the basis of whether communication is real-time or not.Therefore, a radio LAN system can transmit and receive information ofthe kind needing real-time communication, e.g., voice information withminimized delay and quality comparable with the quality of a wired LANsystem. Further, the illustrative embodiments assign a particular datastructure to each of control, voice and data so as to execute even errorcorrection, thereby guaranteeing QoS and saving the limited frequencyband. The radio LAN system therefore reduces interference, promotes theeffective use of frequency, and insures signal QoS.

In summary, it will be seen that the present invention provides a radioLAN system allowing an access point and a station to communicate witheach other without any interference between spread information signalsassigned to different channels. The radio LAN system can therefore sendor receive different types of data, e.g., real-time voice andnon-real-time usual data at the same time. The radio LAN system of thepresent invention reduces interference, promotes effective use offrequency, and guarantees signal QOS.

The entire disclosure of Japanese patent application No. 2001-135182filed on May 2, 2001, including the specification, claims, accompanyingdrawings and abstract of the disclosure is incorporated herein byreference in its entirety.

While the present invention has been described with reference to theparticular illustrative embodiments, it is not to be restricted by theembodiments. It is to be appreciated that those skilled in the art canchange or modify the embodiments without departing from the scope andspirit of the present invention.

1. An access point forming a limited service area for a radio LAN (LocalArea Network), said access point comprising: a transmitter for spreadingan information signal in a direct spread spectrum system, which spreadsa frequency band width of the information signal, and transmitting aspread information signal; and a receiver for receiving the spreadinformation signal and inversely spreading said spread informationsignal; said transmitter comprising: a plurality of informationtransmitting circuits each for multiplying, in the direct spreadspectrum system, the information signal and a particular one of aplurality of spread codes; and a transmission controller for selecting,in accordance with at least one of a kind and an amount of theinformation signal, one of a plurality of frequency bands andfrequencies respectively assigned to said plurality of informationtransmitting circuits and one of a plurality of packets to use fortransmission of the information signal, and maintaining transmissionpower of the spread information signal semi-fixed, wherein the kind ofthe information signal is any one of a control packet sent from saidaccess point to a station present in said limited service area, achannel packet for data and a channel packet for voice.
 2. The accesspoint in accordance with claim 1, wherein said control packet comprisesa field storing frame synchronization information of the control packet,an information field identifying said access point, a voice channelinformation field indicative of a channel number available for voice, adata channel information field indicative of a channel number availablefor data, a control information field indicative of various kinds ofrequest control, and a control data field storing error control data ofthe control packet, the control information field storing locationconfirmation request information for requesting confirmation of alocation of said station present in the service area, registrationrequest information for requesting registration of said station newlyentering the service area, call information for requesting communicationfrom said access point to said station, and report informationindicative of channel release.
 3. The access point in accordance withclaim 1, wherein the channel packet for data comprises a field storingframe synchronization information of the channel packet, a destinationinformation field identifying a destination of the information signal, asource information field identifying a source having sent theinformation signal, a storage information field indicative of an amountof data of the information signal stored, a field storing theinformation signal, and a storage field storing error control data ofthe channel packet, each of the destination information field, thesource information field, the storage information field and the storagefield being variable in size.
 4. The access point in accordance withclaim 1, wherein the channel packet for voice comprises a field storingframe synchronization information of the channel packet, a destinationinformation field identifying a destination of the information signal, asource information field identifying a source sent the informationsignal, a storage field storing the information field, and a storagefield storing error control data of the channel packet, each of thedestination information field, the source information field and thestorage fields being fixed in size.
 5. The access point in accordancewith claim 1, wherein said access point further comprises a connectingcircuit for connecting said access point to a radio access apparatus. 6.The access point in accordance with claim 1, wherein said access pointis operable in a TDD (Time Division Duplex) mode particular to anIMT-2000 system.
 7. The access point in accordance with claim 1, furthercomprising an interface for connecting said access point to a wired LAN.8. A wireless station for use in a limited service area of a radio LAN(Local Area Network), said station comprising: a transmitter forspreading an information signal in a direct spread spectrum system,which spreads a frequency band width of the information signal, andtransmitting a spread information signal; and a receiver for receivingthe spread information signal and inversely spreading said spreadinformation signal; said transmitter comprising: a plurality ofinformation transmitting circuits each for multiplying, in the directspread spectrum system, the information signal and a particular one of aplurality of spread codes; and a transmission controller for selecting,in accordance with at least one of a kind and an amount of theinformation signal, one of a plurality of frequency bands andfrequencies respectively assigned to said plurality of informationtransmitting circuits and one of a plurality of packets to use fortransmission of the information signal, and maintaining transmissionpower of the spread information signal semi-fixed, wherein the kind ofthe information signal is any one of a control packet sent from saidstation to an access point, a channel packet for data and a channelpacket for voice.
 9. The wireless station in accordance with claim 8,wherein the control packet comprises a field storing framesynchronization information of the control packet, an information fieldidentifying said station, a field storing error control data of thesecond control packet, and a control information field indicative ofvarious kinds of request control, said control information field storinglocation confirmation acknowledgement information for answering thelocation confirmation request information, registration acknowledgementinformation for answering the registration request information when saidstation newly enters the service area, call acknowledgement informationfor answering the call request information, communication requestinformation for requesting communication with said access point, andreport information indicative of channel release.
 10. The wirelessstation in accordance with claim 8, wherein the channel packet for datacomprises a field storing frame synchronization information of thechannel packet, a destination information field identifying adestination of the information signal, a source information fieldidentifying a source having sent the information signal, a storageinformation field indicative of an amount of data of the informationsignal stored, a field storing the information signal, and a storagefield storing error control data of the channel packet, each of thedestination information field, the source information field, the storageinformation field and the storage field being variable in size.
 11. Thewireless station in accordance with claim 8, wherein the channel packetfor voice comprises a field storing frame synchronization information ofthe channel packet, a destination information field identifying adestination of the information signal, a source information fieldidentifying a source sent the information signal, a storage fieldstoring the information field, and a storage field storing error controldata of the channel packet, each of the destination information field,the source information field and the storage fields being fixed in size.12. The wireless station in accordance with claim 8, wherein saidstation is operable in a TDD (Time Division Duplex) mode particular toan IMT-2000 system.
 13. The wireless station in accordance with claim 8,further comprising an interfacing circuit for connecting said station toeither one of a public switched telephone network and a terminalconfigured, to process the information signal.
 14. A radio LAN (LocalArea Network) system comprising an access point forming a limitedservice area and a station present in the limited service area fortransmitting by radio an information signal between the access point andthe station within the service area: each of said access point and saidstation comprising: a transmitter for spreading the information signalin a direct spread spectrum system, which spreads a frequency band widthof the information signal, and transmitting a spread information signal;and a receiver for receiving the spread information signal and inverselyspreading said spread information signal; said transmitter comprising: aplurality of information transmitting circuits each for multiplying, inthe direct spread spectrum system, the information signal and aparticular one of a plurality of spread codes; and a transmissioncontroller maintaining transmission power of the spread informationsignal at a level that guarantees a minimum value of received fieldstrength without exceeding an upper limit of transmission power andwithout limiting transmission power in any individual one of saidplurality of information transmitting circuits, wherein a kind of theinformation signal is any one of a control packet sent from said stationto said access point, a channel packet for data and a channel packet forvoice.
 15. The system in accordance with claim 14, wherein said accesspoint further comprises a connecting circuit for connecting said accesspoint to a radio access apparatus.
 16. The system in accordance withclaim 14, wherein said access point and said station each are operablein a TDD (Time Division Duplex) mode particular to an IMT-2000 system.17. The system in accordance with claim 14, said access point furthercomprising a first interface for connecting said access point to a wiredLAN.
 18. The system in accordance with claim 14, said station furthercomprising a second interfacing circuit for connecting said station toeither one of a public switched telephone network and a terminalconfigured to process the information signal.